Unsaturated lipids feature double bonds in fatty acid chains

Steps:

• Recall lipid structure: triglycerides consist of glycerol backbone ester-linked to three fatty acid chains.
• Define unsaturation: double bonds (C=C) occur in hydrocarbon chains, reducing saturation.
• Identify location: double bonds form between carbon atoms within fatty acid tails, not in the glycerol or linkages.
• Confirm: saturated lipids lack these bonds; unsaturated ones (e.g., oils) have them only in fatty acids.

Why B is correct:

• Unsaturated fatty acids contain one or more C=C double bonds within their carbon chains, as per organic chemistry definitions of alkene functional groups.

Why the others are wrong:

• A: Linkages between fatty acids and glycerol are single covalent ester bonds, with no double bonds.
• C: Glycerol is a saturated three-carbon polyol with only single bonds.
• D: Glycerol lacks double bonds, so inclusion is inaccurate.

Final answer: B